I've used two outdoor Nest cams for several years. They've been dormant for a few months. I tried to reconnect them today via iOS -- same wifi, same cameras, same placement: absolutely zero changes -- and kept getting a range of "C" error codes: "couldn't connect to Nest - your wifi router is not connected to the internet". Of course my router is connected to the internet - it's humming along, running plenty of devices at full throttle. So I rebooted the cameras, the router, the cameras AND the router. Multiple times. Nada.
Next I moved on to Option 2, as prompted by the phone app -- connect the camera via computer -- and found Nest's Mac connection software dates from 2015. Seriously. It can't even execute - how shocking! Apple suggests contacting the app developer for an update. Hello Nest, is anyone listening? Nest literally directs users to its own obsolete software. There is thus no way a mac user can connect the cameras via computer.
After some research I found at least a dozen recent posts here with the same problem. The old Nest Outdoor wired cams (not IQ) simply no longer connect to many routers.
The most maddening part is the responses from the "community specialists" here - generally days to weeks after the original poster requests help. Of course, the OP is long gone by then. They've doubtless dumped the bricked cameras in the trash, and moved on to another brand that a) actually works and b) values its customers. The 'community specialist' then closes the thread due to lack of activity. D'oh.
This is without question the worst case of planned obsolescence and disregard for customers I've seen in a very long time.
For the record, my internet is 1G fiber. All my devices are recent models running the latest OS. I have iPv6 enabled. Apparently these Nests need 2.4GHz (hello, 2015!) connections. My household uses an Eero mesh network that defaults to the strongest band, so I performed a manual downgrade to 2.4GHz. Didn't help.
Did I mention planned obsolescence? Now I'm off to buy a camera that actually works.
